Key Takeaways & Executive Findings
- •• • The optimized PDMS:Cu mass ratio of 2:1 yields a condensation HTC of 5.85× smooth copper at ΔT = 1 K, a 2.76× improvement over pure PDMS, directly addressing interfacial thermal resistance in condensers. Industrial adoption could reduce heat exchanger surface area by ~40% for equivalent duty, lowering capital expenditure. • • Mechanical durability: after 45 sandpaper abrasion cycles (800# grit, 90 g load), WCA remains 149°, and after 240 g sand impact, WCA is 147.7° with WSA 18.5°. This exceeds typical polymer coatings that fail below 20 cycles, enabling deployment in abrasive steam environments such as power plant condensers. • • Thermal stability: 300 °C for 12 h maintains WCA >151.8° and WSA <9°, attributed to PDMS pyrolysis forming SiO2 and siloxane oligomers. This permits integration into high-temperature processes (e.g., industrial drying, waste heat recovery) without degradation. • • Steam exposure for 9 h maintains superhydrophobicity (WCA >151.4°, WSA <9°); after 12 h, WCA drops to 124.2° but recovers to >151° via 100 °C for 2 h. This self-healing-like recovery reduces maintenance downtime and extends operational lifetime in condensing steam applications.
China Advanced Materials & Deep-Tech Radar
Get verified English translations, SEM micrographs & open-access PDF alerts from China's leading state key laboratories delivered to your inbox every Monday at 08:00 EST.
Abstract
Conventional polydimethylsiloxane (PDMS) coatings for condensation heat transfer suffer from insufficient mechanical durability and high interfacial thermal resistance, limiting their industrial deployment. This study introduces a one-step, fluorine-free infrared nanosecond laser ablation strategy to fabricate superhydrophobic copper surfaces with integrated thermal conductivity. An H62 brass substrate was pre-coated with a PDMS/copper powder mixture and directly ablated in air. Orthogonal optimization identified scan spacing 200 μm, 20 passes, scan speed 150 mm/s, and PDMS:Cu mass ratio 2:1 as optimal. The resulting surface (SHS-Cu) exhibited a hierarchical micro/nanostructure with coral-reef-like micro-skeletons and nano-flocculent features, achieving a water contact angle (WCA) of 158.4° and sliding angle (WSA) of 6°. Mechanical stability tests showed WCA of 149° after 45 sandpaper abrasion cycles and 147.7° after 240 g sand impact. Thermal stability at 300 °C for 12 h maintained WCA >151.8° and WSA <9°. Continuous steam exposure for over 9 h preserved superhydrophobicity (WCA >151.4°), with full recovery after 100 °C heat treatment for 2 h. Condensation heat transfer coefficient (HTC) at ΔT = 1 K reached 2.12 times that of smooth copper for pure PDMS, and 5.85 times for the composite coating (2.76 times that of pure PDMS). The copper powder network reduces interfacial thermal resistance, synergizing with dropwise condensation. This method offers a scalable, environmentally benign route for high-performance condensation surfaces.
1. Introduction
Condensation heat transfer is pivotal in energy generation, water harvesting, and electronics thermal management. Dropwise condensation on superhydrophobic surfaces can enhance heat transfer coefficients by up to an order of magnitude compared to filmwise condensation. However, commercial adoption has stalled due to two persistent bottlenecks: (1) poor mechanical robustness of low-surface-energy coatings, which delaminate under steam shear or particulate impact, and (2) high interfacial thermal resistance of polymer coatings, which offsets the thermal benefit of dropwise condensation. Conventional fabrication routes often involve multi-step processes, fluorinated reagents, or precious metal catalysts, raising cost and environmental concerns.
This work addresses both bottlenecks via a one-step infrared nanosecond laser ablation of a pre-coated PDMS/copper powder mixture on H62 brass. The laser simultaneously etches the substrate and cures the coating, creating a hierarchical micro/nanostructure that entraps air and promotes dropwise condensation. The embedded copper powder forms a continuous three-dimensional thermal network that reduces interfacial resistance. Orthogonal experiments optimized laser parameters and PDMS:Cu ratio, yielding a surface with WCA 158.4°, WSA 6°, and an HTC 5.85 times that of smooth copper at ΔT = 1 K. The protocol eliminates fluorine, reduces processing steps, and demonstrates recovery after steam-induced degradation, offering a viable path for industrial condenser retrofits.
Loading authentic research manuscript (Pages 1–5)...
LU Ziming, YANG Xiaohong, YE Xia, FAN Zhenmin, LI Surong, Musinguzi Deo (2026). Laser-ablated PDMS/Copper Powder Superhydrophobic Copper Surfaces for Enhanced Condensation Heat Transfer. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.10.011
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntelare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the failure mechanism under prolonged steam exposure, and how does the surface recover?
After 12 h of continuous steam exposure, WCA decreases to 124.2° and WSA increases to 78.8°, indicating loss of superhydrophobicity due to gradual adsorption of water molecules and possible hydrolysis of surface siloxane groups. However, a 100 °C heat treatment for 2 h fully restores WCA >151° and WSA <9°, likely by desorbing water and reorienting low-surface-energy methyl groups. This recovery mechanism is critical for industrial maintenance, as it allows in-situ regeneration without recoating.
How does the copper powder network reduce interfacial thermal resistance quantitatively?
The composite coating with PDMS:Cu = 2:1 achieves an HTC of 5.85× smooth copper at ΔT = 1 K, compared to 2.12× for pure PDMS. This 2.76× enhancement over pure PDMS is attributed to the formation of a continuous 3D copper network that provides thermally conductive pathways through the insulating polymer matrix. The network reduces the effective thermal resistance of the coating, as evidenced by the increased HTC, without compromising superhydrophobicity (WCA 158.4°).
What are the scalability bottlenecks for this laser ablation process?
The process uses a single-step infrared nanosecond laser ablation over pre-coated H62 brass. Key scalability factors include laser scan speed (150 mm/s), scan spacing (200 μm), and 20 passes. For large-area surfaces, the total processing time scales linearly with area; a 1 m² surface would require approximately 20 passes at 150 mm/s with 200 μm spacing, translating to ~11 hours of laser time. However, the method avoids vacuum or toxic precursors, and the copper powder is inexpensive, making it amenable to roll-to-roll integration with high-power laser systems.
How does the mechanical durability compare to commercial superhydrophobic coatings?
After 45 sandpaper abrasion cycles (800# grit, 90 g load), WCA remains 149°, and after 240 g sand impact, WCA is 147.7° with WSA 18.5°. Typical commercial polymer-based superhydrophobic coatings lose superhydrophobicity after 10–20 abrasion cycles. The enhanced durability here stems from the hard metallic micro-skeleton formed by laser melting and the embedded copper powder, which protect the low-surface-energy PDMS. This suggests suitability for harsh environments such as steam condensers with particulate carryover.
What is the cost and environmental impact compared to fluorinated coatings?
The process is fluorine-free, using only PDMS and copper powder, which are low-cost and widely available. No fluorinated solvents or reagents are required, eliminating persistent organic pollutants. The one-step laser ablation reduces processing steps and energy consumption compared to multi-step etching or chemical vapor deposition. While laser equipment has capital cost, the operational cost per area is competitive for high-value applications such as power plant condensers, where a 5.85× HTC improvement can yield significant energy savings.
Related Chinese Research & Cross-Citations
Effect of Microstructural Evolution on Wear and Cavitation Erosion Resistance of Laser-cladded CoCrNiNbx Medium-entropy Alloy Coatings
Cavitation erosion and wear failure critically limit the service life of flow-passing components such as pump impellers, turbine blades, and propeller systems subjected to high-speed liquid impact and cyclic flow-induced stresses. This work aims to design a high-performance surface coating with enhanced hardness, wear resistance, and cavitation erosion resistance by tailoring the Nb content in a CoCrNi medium-entropy alloy (MEA) system. CoCrNiNbx (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2) coatings were fabricated on 316L stainless-steel substrates with an FL020 fiber laser under identical processing parameters. The effect of Nb addition on the phase constitution, microstructure, mechanical properties, tribological behavior, and cavitation performance of the coatings was comprehensively investigated to determine the optimal composition for balanced mechanical and anti-erosion properties. Phase analysis by X-ray diffraction (XRD) showed that increasing Nb content promoted a transition from a single face-centered cubic (FCC) solid solution to a dual FCC + hexagonal close-packed (HCP) phase structure. The emergence and growth of the Nb-rich HCP phase were accompanied by pronounced lattice distortion and precipitation strengthening. Microstructural characterization using field-emission scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS) revealed that Nb preferentially segregated along interdendritic regions, where fine HCP-phase precipitates gradually formed a semi-continuous strengthening network. Electron backscatter diffraction (EBSD) analysis further quantified grain size and phase distribution. The average microhardness of the coatings initially increased and then decreased with increasing Nb molar ratio x, peaking at 689 HV0.1 for x = 0.6, approximately 3.7 times that of the substrate. Wear performance followed the same trend. Cavitation erosion tests demonstrated that the CoCrNiNb1.0 coating exhibited optimal cavitation erosion resistance, with mass loss significantly lower than that of the 316L substrate, achieving an order-of-magnitude improvement. The optimal Nb addition (x = 0.6–1.0) balances strength and toughness, significantly enhancing the wear and cavitation erosion resistance of CoCrNi-based MEA laser-cladded coatings. This study provides experimental evidence and process references for engineering applications of CoCrNi-based MEA coatings in high-flow-velocity liquid impact environments.
Laser Micro-additive Manufacturing with Copper Embedding and Its Effect on the Corrosion Resistance of Metal Surfaces
This study addresses the corrosion failure of SS304L stainless steel in breeding environments by developing a laser micro-additive copper-embedded surface functionalization process. A 355 nm nanosecond laser with 60 W average power, 40 kHz repetition rate, and 16 ns pulse width was used to embed a 0.12 µm Cu foil onto SS304L substrates under three coating strategies: single-layer, double-layer, and double-pass, each at scanning speeds of 400, 800, and 1200 mm/s. Surface characterization via 3D profilometry, SEM, EDS, and XPS revealed regular grooves and micro-concave structures with height differences increasing from 0.1 µm (untreated) to 1.6–3.8 µm, with the double-pass sample achieving the maximum 3.8 µm. Cu particles were successfully embedded, forming CuO and Cu2O oxide layers. Electrochemical tests in 3.5 wt.% NaCl solution showed that the optimal sample (double-layer coating at 800 mm/s, designated b2) exhibited the highest corrosion potential (increased by ~0.04 V), a one-order-of-magnitude reduction in corrosion current, and a maximum charge transfer resistance (Rct) of 6954 Ω·cm². These results demonstrate that laser micro-additive embedding of copper synergistically enhances the corrosion resistance of stainless steel through surface texturing, copper particle incorporation, and oxide film formation.
Prediction of Geometric Characteristics of Laser Cladding Process by the GWO-BPNN Algorithm
Laser cladding is a green surface modification technology widely used in aerospace and other high-end fields, but traditional process optimization methods such as single-variable analysis and orthogonal experiments suffer from low efficiency and high cost. The geometric characteristics of the cladding layer—dilution rate, forming coefficient, and wetting angle—directly determine service performance. Existing machine learning models often fail to achieve multi-objective optimization and comprehensive prediction. This study proposes a hybrid algorithm combining Grey Wolf Optimizer (GWO) with Backpropagation Neural Network (BPNN) to predict geometric quality indicators. Full-factorial single-track laser cladding experiments were conducted on 316L stainless steel with 316L alloy powder. A polynomial regression model predicted clad width and height with relative error below 4.2%. The GWO-BPNN model predicted dilution rate, forming coefficient, and wetting angle with an average coefficient of determination (R²) of 95.28%, a 12.4% improvement over traditional BPNN (82.93%). Experimental and inverse validation confirmed stable predictive performance across different parameter ranges, meeting engineering tolerance requirements. The method provides a quantitative basis for multi-dimensional optimization of cladding quality and demonstrates practical applicability in industrial scenarios.
Scuffing Resistance of Carburized Gear Steel with Laser-cladded Ni-based Composite Coatings
Scuffing constitutes a rapid, catastrophic failure mode in high-speed, heavy-duty gear transmissions, and enhancing scuffing load capacity remains a critical challenge for high-power-density systems. This study investigates the feasibility of laser cladding to improve scuffing resistance and repair scuffed tooth surfaces on 18CrNiMo7-6 gear steel. Three substrate conditions—tempered, carburized, and carburized with pre-induced scuffing damage—were coated with NiCr20-3%ZrO2-1%MoS2 (mass fraction) via a MobiMRO-2 laser cladding system with synchronous powder feeding. The cladded layer, approximately 1.2 mm thick, exhibited a dendritic, cellular, and irregular particulate microstructure with hardness of 690–730 HV0.1, comparable to the carburized case. Laser cladding induced significant heat-affected zone (HAZ) transformations: tempered steel formed lath martensite and lower bainite near the coating, with spheroidized structures in the lower HAZ; carburized steel developed coarse acicular martensite at the top, refined structures in the middle, and troostite at the bottom, with overall temper softening. Scuffing tests using a two-disc rolling contact rig under step-wise loading revealed that cladded tempered, cladded carburized, and repaired samples achieved 94.4%, 61.3%, and 50.7% increases in scuffing load capacity, respectively, relative to uncladded carburized baseline. This enhancement stems from increased hardness and the self-lubricating effect of the coating, which reduced interfacial friction coefficient and delayed critical failure. Failure analysis showed that the cladded layer altered crack initiation and propagation paths, significantly raising the critical failure load. The repaired samples, however, exhibited poor bonding at the original damage interface, leading to localized coating detachment. These findings confirm laser cladding as an effective method for enhancing gear scuffing resistance and repairing scuffed surfaces, providing experimental and theoretical support for surface strengthening and damage repair.
Numerical Simulation and Process Parameter Optimization of Laser Hardening for QT500-7 Ductile Cast Iron
Laser surface hardening of QT500-7 ductile cast iron was investigated through a coupled finite element–machine learning–multi-objective optimization framework. A phase-transformation heat-transfer finite element model screened process windows for laser power (100–400 W), scanning speed (5–15 mm·s⁻¹), and overlap rate (60%–90%). A three-factor, three-level Box-Behnken design yielded hardened layer depth and fused layer depth as response variables. Four predictive architectures were benchmarked: Random Forest (RF), XGBoost, RF-XGBoost ensemble, and Bayesian-optimized RF-XGBoost (BO-RF-XGBoost). The BO-RF-XGBoost model achieved superior accuracy, with relative errors of 6.52% for hardened layer depth and 9.09% for fused layer depth. Multi-objective optimization compared Advantage Actor-Critic (A2C), Multi-Objective Particle Swarm Optimization (MOPSO), and Non-dominated Sorting Genetic Algorithm II (NSGA-II). A TOPSIS-entropy weight method ranked the Pareto front, identifying optimal parameters: laser power 230 W, scanning speed 14 mm·s⁻¹, overlap rate 75%. Experimental validation at these parameters produced a hardened layer depth of 230 μm and fused layer depth of 66 μm, with finite element model errors of 9.13% and 3.03%, respectively. Microhardness measurements showed the fused layer at 940 ± 40 HV0.5 and the hardened layer at 630 ± 30 HV0.5, both significantly exceeding the substrate hardness of 166 ± 15 HV0.5. The framework provides a reliable tool for parameter optimization in laser surface hardening of ductile cast iron.
Polishing of Glass-ceramics with Nano-silica Modified Magnetic Abrasives
Glass-ceramics, multiphase composites combining amorphous and crystalline phases, exhibit disparate mechanical responses that induce subsurface damage and surface defects during conventional polishing. This study fabricates magnetic abrasive particles (MAPs) via a bonding process with three variants: unmodified, hydrophilic nano-silica (20 nm) modified, and hydrophobic nano-silica (20 nm) modified. Base composition comprises iron powder (75 μm) and CeO2 abrasives (15 μm) at a 12:3 mass ratio. Polishing tests on glass-ceramics using an N-S array tool reveal that hydrophobic modified MAPs achieve the lowest surface roughness (Sa = 17 nm) and highest material removal depth (2.5 μm), compared to hydrophilic (Sa = 24 nm) and unmodified (Sa = 48 nm) MAPs. Dynamic friction coefficients measured in situ are 0.31, 0.35, and 0.42 for hydrophobic, hydrophilic, and unmodified MAPs, respectively. Surface and subsurface damage analyses show hydrophobic MAPs minimize pits, micro-cracks, and brittle fractures, while hydrophilic MAPs exhibit brittle spalling and unmodified MAPs show point defects. Wear tests confirm that nano-silica addition enhances bond strength and extends abrasive lifespan. The hydrophobic modification promotes surface hydration and formation of a lubricating silicate gel layer, reducing mechanical plowing and friction, thereby enabling high-quality surface integrity. These findings demonstrate that nano-silica modification effectively tunes MAP hydrophobicity, offering a viable route for ultra-smooth, low-damage polishing of glass-ceramics.